Vocal specialization through tracheal elongation in an extinct Miocene pheasant from China

Zhiheng Li,Tao Deng,Thomas A Stidham,Zhonghe Zhou,Julia A Clarke,Chad M Eliason

doi:10.1038/s41598-018-26178-x

Abstract

Modifications to the upper vocal tract involving hyper-elongated tracheae have evolved many times within crown birds, and their evolution has been linked to a ‘size exaggeration’ hypothesis in acoustic signaling and communication, whereby smaller-sized birds can produce louder sounds. A fossil skeleton of a new extinct species of wildfowl (Galliformes: Phasianidae) from the late Miocene of China, preserves an elongated, coiled trachea that represents the oldest fossil record of this vocal modification in birds and the first documentation of its evolution within pheasants. The phylogenetic position of this species within Phasianidae has not been fully resolved, but appears to document a separate independent origination of this vocal modification within Galliformes. The fossil preserves a coiled section of the trachea and other remains supporting a tracheal length longer than the bird’s body. This extinct species likely produced vocalizations with a lower fundamental frequency and reduced harmonics compared to similarly-sized pheasants. The independent evolution of this vocal feature in galliforms living in both open and closed habitats does not appear to be correlated with other factors of biology or its open savanna-like habitat. Features present in the fossil that are typically associated with sexual dimorphism suggest that sexual selection may have resulted in the evolution of both the morphology and vocalization mechanism in this extinct species.

Highlights

A key characteristic of most living birds is their ability to vocalize and produce a variety of sounds for acoustic signaling and communication
Sounds produced by the syrinx may be modified by the upper vocal tract, including the shape of the oropharyngeal cavity affected by the mouth and tongue[6,7], tracheal bullae[8,9] and modifications to the diameter of the trachea, expansion of the esophagus while vocalizing[5,7,10], and significant tracheal elongation (TE) where the trachea forms permanent coils or loops[11,12]
In addition to Tetraoninae, this taxon represents the third record of elongation of the trachea in Phasianidae and the first within Phasianinae, a diverse group including over 150 extant species of pheasants, peafowl, francolins, and others

Summary

Introduction

A key characteristic of most living birds is their ability to vocalize and produce a variety of sounds for acoustic signaling and communication. Positive selection for a longer trachea may occur in birds to compensate for limited nasal turbinate sizes, aiding in the reduction of evaporative heat and water loss[16] This hypothesis does not appear to explain its absence in birds of similar ecologies to those exhibiting TE or dimorphism in the trait within a single species. In addition to Tetraoninae, this taxon represents the third record of elongation of the trachea in Phasianidae (besides Tetrao urogallus and Lagopus mutus) and the first within Phasianinae, a diverse group including over 150 extant species of pheasants, peafowl, francolins, and others This new species from the Miocene deposits of Gansu Province adds new data to the ecological diversity of this extinct steppe-dwelling avifauna at the edge of the Tibetan Plateau that includes an extinct long-legged kestrel, ostrich, and Old World vultures[20,21,22,23]

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